The present invention relates to a surface coating composition that is characterized by moisture and chemical resistance and a method of imparting such characteristics to a surface coating composition.
Metal oxides, particularly dry silica gels, have been incorporated into certain surface coating materials in order to achieve the impression of xe2x80x9cmattness.xe2x80x9d A wet film applied to a substrate is initially held flat and therefore glossy by the forces of surface tension. As the film dries and cures, the increasing viscoelasticity associated with the sol-gel transition hinders the movement of particles into the film, and the surface deforms to accommodate the matting agent particles. This roughness is maintained in the solidified film, which then is characterized by a matt finish. While the matting effect attributable to certain silica gels produces a desirable surface appearance for some applications, a surface coating composition desirably possesses additional properties, such as moisture resistance, in order to enhance its utility for a variety of applications.
Moisture resistance is a characteristic of a composition such that the composition resists damage after wetting by or absorption of water. Prior attempts at rendering a surface coating composition moisture resistant have focused on the hydrophobic modification of the silica aerogel. Silica xerogels, for example, have been rendered hydrophobic by esterification with organic alcohols at high temperatures or by physical adsorption of organic polymers. While such agents may impart a degree of hydrophobicity to the silica aerogel, these surface materials remain reactive and can be lost from the xerogel in the presence of other reactive species, such as alcohols and water. The moisture resistance properties imparted to the composition by the silica gel, if any, can be accordingly degraded when the composition is exposed to other chemical agents. Such exposure to other chemical agents, such as alcohols, often occurs when the composition is a surface coating, such as a coating on wood furniture.
Thus, there remains a need for surface coating compositions that provide a matting effect while also imparting moisture and chemical resistance to substrates. The present invention seeks to provide such a surface coating composition. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
The present invention provides a surface coating composition comprising a resin system, and a hydrophobic metal oxide, wherein said composition, after application to a substrate, is characterized by (a) a moisture resistance which is retained for at least about 6 months, (b) a resistance to a 50% w/w ethanol/water solution, and (c) a gloss level of about 50 gloss units or less.
The present invention also provides a method of matting a surface coating composition and enhancing the moisture and chemical resistance of the composition comprising (i) providing a hydrophobic metal oxide which imparts to the composition, after application to a substrate, (a) a moisture resistance which is retained for at least about 6 months, (b) a resistance to a 50% w/w ethanol/water solution, and (c) a gloss level of less than 50 gloss units, and (ii) mixing the metal oxide with a resin system to form the surface coating composition.
The present invention further provides a substrate having a surface coated with the surface coating composition of the present invention, as well as a method of treating a substrate with the present inventive surface coating composition.
The present invention provides a surface coating composition comprising a resin system, and a hydrophobic metal oxide. The composition, after application to a substrate, is characterized by (a) a moisture resistance which is retained for at least about 6 months, (b) a resistance to an organic alcohol solution, particularly a resistance to a 50% w/w ethanol/water solution, and (c) a gloss level of 50 gloss units or less.
The resin system can comprise any suitable resin. Thus, the resin can be any resin known by those of skill in the art to be suitable for use in a surface coating composition. Suitable resins include, for example, polyesters, epoxies, urethanes, cellulosics, alkyds, acrylics, and mixtures and precursors thereof. Suitable acrylic resins for use in the composition of the present invention include those known as WORLEE CRYL A 1220 (E.H. Worlee and Co., Germany) and NEOCRYL A-633 (Zeneca Resins, Wilmington, Mass.).
Preferably, the resin is a nitrocellulose or a nitrocellulose alkyd. Suitable nitrocellulose resins include LANCO CL-600 (Lanco Manufacturing Corporation, San Lorenzo, Calif.), and cellulose nitrate. Among the useful alkyd resins are those known as WORLEEKYD T36 (E.H. Worlee and Co, Germany).
Any suitable amount of resin can be present in the surface coating composition. The resin is preferably present in the surface coating composition in an amount of about 10-95% w/w.
Any suitable metal oxide can be used in the context of the present invention. Suitable metal oxides include silica, alumina, titania, zirconia, ceria, and magnesia. The metal oxide preferably is silica, such as, for example, fumed (or pyrogenic) silica, precipitated silica, or silica aerogel, with silica aerogel being particularly preferred. The term xe2x80x9caerogelxe2x80x9d refers to a substantially amorphous organic or inorganic gel with air in the pores. Most preferably, the aerogel comprises silica and is prepared by modifying the surface of a hydrogel with a silylating agent and drying the surface-modified gel. The silica aerogel produced by this process may be partially or completely hydrophobic depending on the degree and type of silylation. The silica aerogels disclosed in WO 98/23366 are especially desirable as the metal oxide in the surface coating composition of the present invention.
The treated metal oxide has a hydrophobic character. Any suitable hydrophobic moiety may be bonded to the metal oxide of the present invention to obtain the effect. Suitable hydrophobic moieties are derived, for example, from compounds of the following general formulae:
R3Si-O-SiR3xe2x80x83xe2x80x83(I)
R3Si-N(H)-SiR3xe2x80x83xe2x80x83(II)
Wherein the radicals R are identical or different and are each hydrogen or a nonreactive, organic, linear, branched, cyclic, saturated or unsaturated, aromatic or heteroaromatic radical, preferably C1-C18 alkyl or C6-C14 aryl, more preferably C1-C6 alkyl, cycloalkyl, phenyl, vinyl, or acryl. Equally suitable hydrophobic moieties can be derived from silanes of the formulae R14-nSiCln or R14-nSi(OR2 )r, where n=1-4, and R1 and R2 are identical or different and are each hydrogen or a nonreactive, organic, linear, branched, cyclic, saturated or unsaturated, aromatic or heteroaromatic radical, preferably a C1-C18 alkyl or C6-C14 aryl, and more preferably a C1-C6 alkyl, cyclohexyl, or phenyl. The radicals may also contain halogen substituents, such as fluorine or chlorine. Most preferably, the hydrophobic moiety is a trimethyl silyl, a vinyl dimethyl silyl, a acryl dimethyl silyl, or a dimethyl dicholor silyl.
The metal oxide preferably is characterized by a degree of hydrophobicity of at least about 40% v/v. The degree of hydrophobicity desirably is as high as possible inasmuch as a higher degree of hydrophobicity generally provides improved water resistance.
The term xe2x80x9cdegree of hydrophobicityxe2x80x9d refers to the ratio by volume of methanol in a water-methanol mixture that wets the silica aerogel, thereby forming a homogeneous suspension.
The metal oxide can be in the form of discrete individual particles, which can be in aggregated or non-aggregated form. The metal oxide particles can have any suitable diameter. Generally, the metal oxide has a median particle diameter of about 1-15 xcexcm (e.g., 2-15 xcexcm), preferably 2-10 xcexcm. The particle size of the metal oxide should be sufficient to impart a desirable matting effect to the surface coating composition.
The metal oxide can have any suitable surface area. Generally, the metal oxide has a surface area of at least about 100 m2/g, preferably at least about 200 m2/g, and most preferably at least about 300 m2/g. The metal oxide also can have any suitable particle density, such as about 0.1-0.3 g/cm3.
The metal oxide can have any suitable porosity. Typically the metal oxide has a porosity of at least 50%, preferably about 70% or more, and most preferably about 80% or more.
The metal oxide can be present in the surface coating composition in any suitable amount. For example, the metal oxide can be present in the surface coating composition in an amount of about 0.5-10% w/w.
Optionally, any suitable carrier (e.g., solvent) can be used in the surface coating composition. A carrier is used to facilitate the application of the resin and metal oxide onto the surface of a suitable substrate. Suitable carriers include water, alcohols, ketones, esters, ethers, aromatics, alkyls, and mixtures thereof. Any suitable concentration of carrier can be present in the surface coating composition, such as up to about 80% w/w.
The surface coating composition of the present invention also can include any of a variety of components that are known in the art to be suitable for incorporation into a surface coating composition. Such components include colorants, pigments, UV stabilizers, coalescing agents, flow additives, defoamers, surfactants, rust inhibitors, and pH adjustment agents.
The coalescing agent promotes the softening of the resin during drying of the components of the surface coating composition, and such materials are well known. One example of a coalescing agent is butyl CELLOSOLVE (ARCO Chemical Company, Newtown Square, Pa.). Any suitable concentration of coalescing agent can be present in the surface coating composition, such as about 1-35% w/w.
The flow additive promotes the wetting of the substrate by the surface coating composition and the levelling of the surface coating composition. A typical flow additive is DISBERBYK 301 (BYK-Chemie, Germany). Any suitable concentration of flow additive can be present in the surface coating composition, such as about 0.5-4% w/w.
A defoamer can be added to reduce the presence of bubbles in the surface coating composition upon mixing of the components. Any suitable defoamer can be used in the surface coating composition of the present invention. One preferred defoamer is DISBERBYK 035 (BYK-Chemie, Germany). Any suitable concentration of defoamer can be present in the surface coating composition, such as about 0.01-3% w/w.
A surfactant can be added to reduce the surface tension of the coating composition. Any suitable surfactant can be used in the surface coating composition of the present invention. One preferred surfactant is SURFYNOL 104 BC (Air Products and Chemicals, Inc.). Any suitable concentration of surfactant can be present in the surface coating composition, such as about 0.01-3% w/w.
If the surface coating composition is applied to surfaces vulnerable to corrosion, a rust inhibitor may be added to the composition. A variety of rust inhibitors are suitable for the present invention. One preferred rust inhibitor is ammonium benzoate. Any suitable concentration of rust inhibitor can be present in the surface coating composition, such as about 0.01-2% w/w.
A pH adjustment agent can be added to control the pH of the surface coating composition. The pH of the composition is maintained in a range generally suitable for surface coating compositions. Any suitable pH adjustment agent can be used in the surface coating composition of the present invention. One preferred pH adjustment agent is ammonium hydroxide. Any suitable concentration of pH adjustment agent can be present in the surface coating composition, such as about 1-4% w/w.
The surface coating composition retains its moisture resistance for at least 6 months, preferably for at least 1 year, and most preferably for at least 2 years. Moisture resistance can be determined by visibly examining the extent (if any) of discoloration (generally, white chalky appearance) of a surface coated with the surface coating composition of the present invention after (approximately 16 hours) the application of cold water (15-20 drops) to the surface. The surface coating composition of the present invention preferably demonstrates no discoloration after the application of water to the coated surface.
Despite the ability of the surface coating composition of the present invention to remain soluble or dispersed in an organic alcohol solvent system, it has been discovered that the surface coating composition, after application to a substrate, resists discoloration upon addition of an organic alcohol solution. Indeed, with relatively concentrated organic alcohol solutions, i.e., about 50-70% w/w, the surface coating composition, after application to a substrate, demonstrates only a slight change in appearance. The degree of resistance can be measured by applying the surface coating composition to a substrate, particularly a black Leneta chart, and allowing it to dry thereon so as to form a 40 xcexcm film of the surface coating composition on the substrate. About 7 drops of an alcohol solution, particularly a solution containing 50% w/w ethanol and 50% w/w water, then is placed on the surface of the film, and the alcohol solution on the surface of the film is covered with a watch glass. After approximately 16 hours, the liquid is removed and the substrate is examined visually to determine the extent of discoloration (usually in the form of a white chalky appearance) of the surface of the substrate or of the coating.
Preferably the surface coating composition of the present invention, after application to a substrate, is characterized by a resistance to an organic alcohol solution, particularly a 50% w/w ethanol in water solution, such that only a slight visible discoloration appears after application of the organic alcohol solution to the coated substrate. More preferably the resistance to an organic alcohol solution is such that no visible discoloration appears after application of the alcohol solution to the coated substrate. Accordingly, as used herein, xe2x80x9ca resistance to a 50% w/w ethanol/water solutionxe2x80x9d refers to the absence of or only slight appearance of a visible change (usually in the form of discoloration) to the surface characteristics of the coated substrate (black Leneta chart), which is coated with a 125 xcexcm film (wet) of the surface coating composition of the present invention, after application of an ethanol/water solution containing 50% w/w ethanol and 50% w/w water as described above.
The surface coating composition of the present invention, after application to a substrate, is also characterized by a matting effect. Preferably the surface coating composition is characterized by a gloss level of 50 gloss units or less (as measured by a BYK-Gardner gloss meter). More preferably the surface coating composition is characterized by a gloss level of 40 gloss units or less (e.g., 30 gloss units or less). Matt surfaces are desirable for many applications. For example, the reduced glare of surfaces in schools, hospitals, and universities offers less chance of visual distraction, and concentration is better in such environments. Such finishes also demonstrate less tendency to become unsightly as time progresses, as small scratches and imperfections are less obvious than on gloss surfaces. Finally, matt finishes may create visually appealing surfaces on wood.
The present invention also provides a method of matting a surface coating composition and enhancing the moisture and chemical resistance of the composition comprising (i) providing a hydrophobic metal oxide which imparts to the composition, after application to a substrate, (a) a moisture resistance which is retained for at least about 6 months, (b) a resistance to an organic alcohol solution, and (c) a gloss level of 50 gloss units or less, and (ii) mixing the metal oxide with a resin to form the surface coating composition. optionally, the resin and metal oxide can be mixed together with a carrier. The resin, hydrophobic metal oxide, carrier, and composition characteristics are as described above with respect to the present inventive surface coating composition.
The present invention also encompasses a substrate having a surface coated with the surface coating composition disclosed herein. Any substrate suitable for the application of a surface coating composition is contemplated by the present invention. Such substrates include wood, plastics, clothing (e.g., leather goods), metal, and upholstery (e.g., automotive interior surfaces). Preferably the substrate is a porous surface, such as wood.
A substrate can be treated with the surface coating composition by any suitable technique. For example, the surface coating composition can be applied to the substrate by brushing or by spraying.
As the surface coating composition of the present invention, after application to a substrate, is characterized by a resistance to an organic alcohol solution, the composition functions to protect the surface of a substrate, such as furniture, from discoloration after exposure to alcohol solutions (i.e., alcoholic beverages). In addition, the matting effect of the surface coating composition is desirable if a low gloss surface coating is required, as for example, in furniture lacquers and interior paints for the home or office.